High tg monolithic poly(vinyl acetal) sheet

ABSTRACT

A polyvinyl acetal poly(vinyl acetal), such as polyvinyl butyral, resin formulation, a method of extruding poly(vinyl acetal) resins, and related materials and products that provide for monolithic poly(vinyl acetal) sheets and glass panes having high Tg of at least 50° C. and high modulus at acceptable rates as indicated by their high melt flow index. This is made possible by a reduction in the amount of plasticizer while using a low molecular weight resin not to exceed 160,000 to obtain a thermoplastic resin having a high melt flow index and high Tg. The articles made with these monolithic interlayer sheets can be used in applications that require good modulus at outdoor temperatures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser.No.14/563,025, filed Dec. 8, 2014, the contents of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to poly(vinyl acetal) sheets, and moreparticularly to monolithic poly(vinyl acetal) sheets having high glasstransition temperature that can be extruded at reasonable processconditions. The poly(vinyl acetal) sheets having higher Tg can be usedas an interlayer for laminated glass in more demanding structuralapplications that experience higher ambient temperature conditions.

BACKGROUND OF THE INVENTION

Generally, laminated multiple layer glass panels refer to a laminatecomprised of a polymer sheet or interlayer sandwiched between two panesof glass. The laminated multiple layer glass panels are commonlyutilized in architectural window applications, in the windows of motorvehicles, airplanes, trains and other modes of transporting people andgoods, and in photovoltaic solar panels. The first two applications arecommonly referred to as laminated safety glass. The main function of theinterlayer in the laminated safety glass is to absorb energy resultingfrom impact or force applied to the glass, keep the layers of glassbonded even when the force is applied and the glass is broken, andprevent the glass from breaking up into sharp pieces. Additionally, theinterlayer generally gives the glass a much higher sound insulationrating, reduces UV and/or IR light transmission, and enhances theaesthetic appeal of the associated window. In regards to thephotovoltaic applications, the main function of the interlayer is toencapsulate the photovoltaic solar panels which are used to generate andsupply electricity in commercial and residential applications.

The interlayer is generally produced by mixing a polymer resin such aspoly(vinyl acetal) with one or more plasticizers and melt blending ormelt processing the mix into a sheet by any applicable process or methodknown to one of skill in the art, including, but not limited to,extrusion. Other additional additives may optionally be added forvarious other purposes. After the interlayer sheet is formed, it istypically collected and rolled for transportation and storage and forlater use in the multiple layer glass panels, as described below.Interlayer sheets of the appropriate size and thickness are sometimescut, stacked and shipped in such stacks for later use in the multiplelayer glass panels.

The following offers a simplified description of the manner in whichmultiple layer glass panels are generally produced in combination withthe interlayers. First, at least one interlayer sheet, either monolithicor comprising of several coextruded or prelaminated layers (“multilayerinterlayers”), is placed between two substrates, such as glass panels,and any excess interlayer is trimmed from the edges, creating anassembly. It is not uncommon for multiple monolithic interlayer sheetsto be placed within the two substrates creating a multiple layer glasspanel with multiple monolithic interlayers. It is also not uncommon formultilayer interlayer sheets that comprise several coextruded orprelaminated layers or in combination with monolithic interlayer sheetsto be placed within the two substrates creating a multiple layer glasspanel with multilayer interlayers. Then, air is removed from theassembly by an applicable process or method known to one of skill in theart; e.g., through nip rollers, vacuum bag, vacuum ring, vacuumlaminator, or another de-airing mechanism. Additionally, the interlayeris partially press-bonded to the substrates by any method known to oneof ordinary skill in the art. In a last step, in order to form a finalunitary structure, this preliminary bonding is rendered more permanentby a high temperature and pressure lamination process known to one ofordinary skill in the art such as, but not limited to, autoclaving.

A structural poly(vinyl acetal) interlayer, Saflex™ DG41 (a poly(vinylbutyral) polymer having an Mw of about 170,000), is commerciallyavailable for applications in the architectural space. While the glasstransition temperature Tg of DG41 is suitable for many architecturalapplications (˜46° C.), it would be desirable to raise the Tg of theinterlayer to take advantage of a full range of applications it couldhave in the architectural space. Higher Tg products are desirable asthey may be able to cover more demanding architectural applications thatare exposed to consistently higher temperatures, especially those thatrequire high modulus at higher ambient temperatures.

One methodology to increase the Tg of the poly(vinyl acetal) interlayeris to reduce the amount of plasticizer in the poly(vinyl acetal) resin.Reducing the amount of plasticizer, however, decreases the flowabilityof the polymer composition making processing quite difficult. DG41 isalready difficult to process in extrusion owing to its low level ofplasticizer level, at about 20 parts of plasticizer per 100 parts resin.The low plasticizer level in DG41 decreases its flowability, resultingin reduction in melt flowability and manifests itself as a largepressure drop between the head of the extruder or the melt pump to theback face of the die plate with a corresponding drop in extruder outputor capacity. Although the processing of DG41 is difficult, it remains atan acceptable level. However, attempting to increase the Tg of thepoly(vinyl acetal) interlayer by further dropping the amount ofplasticizer will so decrease the flowability of the polymer compositionso as to make its processing unacceptable.

Increasing the plasticizer level assists in improving the polymerflowability, thereby facilitating processing in the extruder manifestingitself as a lower pressure between the extruder head or melt pump to theback face of the die. However, increasing the plasticizer level alsodecreases the Tg of the interlayer.

It would be desirable to provide a poly(vinyl acetal) thermoplasticresin that has both an enhanced Tg and has suitable flowability. Theincrease in Tg cannot be accomplished by a mere drop in the amount ofplasticizer since, as already mentioned, the processing conditionssuffer through large pressure drops resulting in a loss in outputcapacity.

SUMMARY OF THE INVENTION

We have discovered a poly(vinyl acetal) interlayer composition that hasboth an increased Tg and an acceptable flowability, thereby allowing itto be processed through an extruder at reasonable rates.

There is now provided a composition comprising:

-   -   (A) poly(vinyl acetal) resin in an amount of at least 60 wt. %        based on the weight of the composition; and    -   (B) a plasticizer in an amount of at least 5 parts per one        hundred parts of said poly(vinyl acetal) resin;        wherein said interlayer composition has a Tg of at least 46.0°        and a melt flow index (“MFI”) of at least 0.65 grams/10 minutes        when measured at 190° C. at a load of 2.16 kilograms.

There is also provided a composition comprising:

-   -   (A) poly(vinyl acetal) (“poly(vinyl acetal)”) resin having a        weight average molecular weight (Mw) of 160,000 or less, and    -   (B) a plasticizer in an amount of at least 5 parts per one        hundred parts of said poly(vinyl acetal) resin;        wherein said interlayer composition has a Tg of at least 46.0°        C.

In each case, the composition is desirably a monolithic interlayersheet.

There is further provided a process for making a monolithic interlayersheet comprising poly(vinyl acetal), the method comprising:

-   -   (i) providing an extrusion system comprising die and an extruder        having a barrel;    -   (ii) feeding a poly(vinyl acetal) resin and a plasticizer into        the barrel and passing a molten thermoplastic composition        comprising said poly(vinyl acetal) resin and plasticizer through        the extruder and the die to produce an extruded sheet, wherein        the melt flow index (“MFI”) of the molten thermoplastic resin is        at least 0.65 g/10 min when measured at 190° C. at a loading of        2.16 kg, and    -   (iii) cooling said sheet to produce a monolithic interlayer        sheet having a Tg of at least 46.0° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the rigidity as determined by modulus for avariety of poly(vinyl acetal) resins having different Tg values.

FIG. 2 is a diagram of an extrusion system.

FIG. 3 is a graphical illustration of the creep resistance of examples1-6.

DETAILED DESCRIPTION OF THE INVENTION

The term “sheet” or “monolithic sheet” or “monolithic interlayer” is asingle unitary layer or sheet formed from the thermoplastic compositionof the invention. The monolithic interlayer or a sheet can contain acombination of two or more different types of polymers if desired.

There is now provided a composition comprising:

-   -   (A) poly(vinyl acetal) resin in an amount of at least 60 wt. %        based on the weight of the composition; and    -   (B) a plasticizer in an amount of at least 5 parts per one        hundred parts of said poly(vinyl acetal) resin;        wherein said interlayer composition has a Tg of at least 46.0°        and a melt flow index (“MFI”) of at least 0.65 grams/10 min when        measured at 190° C. at a load of 2.16 kilograms.

There is also provided a composition comprising:

-   -   (A) poly(vinyl acetal) (“poly(vinyl acetal)”) resin having a        weight average molecular weight (Mw) of 160,000 or less, and    -   (B) a plasticizer in an amount of at least 5 parts per one        hundred parts of said poly(vinyl acetal) resin;        wherein said interlayer composition has a Tg of at least 46.0°        C.

The composition comprises a poly(vinyl acetal) resin and a plasticizer.Each will be described in more detail.

The poly(vinyl acetal) resin is a thermoplastic resin. It's method ofmanufacture is not limited. It can be produced by known aqueous orsolvent acetalization processes, such as by reacting poly(vinyl alcohol)PVOH with an aldehyde such as butyraldehyde in the presence of an acidcatalyst, followed by separation, stabilization, and drying of theresin. Such acetalization processes are disclosed, for example, in U.S.Pat. Nos. 2,282,057 and 2,282,026 and Vinyl Acetal Polymers, inEncyclopedia of Polymer Science & Technology, 3rd edition, Volume 8,pages 381-399 (2003), the entire disclosures of which are incorporatedherein by reference.

Poly(vinyl acetal) resins typically have a residual hydroxyl content, anester content, and an acetal content. As used herein, residual hydroxylcontent (calculated as PVOH) refers to the weight percent of moietieshaving a hydroxyl group remaining on the polymer chains. For example,poly(vinyl acetal) can be manufactured by hydrolyzing poly(vinylacetate) to PVOH, and then reacting the PVOH with an aldehyde, such asbutyraldehyde, propionaldehyde, and the like-, and desirablybutyraldehyde, to make a polymer having repeating vinyl butyral units.In the process of hydrolyzing the poly(vinyl acetate), typically not allof the acetate side groups are converted to hydroxyl groups. Further,reaction with butyraldehyde typically will not result in the conversionof all hydroxyl groups on the PVOH to acetal groups. Consequently, inany finished poly(vinyl butyral), there typically will be residual estergroups such as acetate groups (as vinyl acetate groups) and residualhydroxyl groups (as vinyl hydroxyl groups) as side groups on the polymerchain and acetal (e.g. butyral) groups (as vinyl acetal groups). As usedherein, residual hydroxyl content is measured on a weight percent basisper ASTM 1396.

An example of a polyvinyl butyral structure is used to furtherillustrate how the weight percentages are based from the moiety unit towhich is bonded the relevant pendant group:

Taking the above structure of a polyvinyl butyral, the butyral or acetalcontent is based on the weight percentage of the unit A in the polymer,and OH content is based on the weight percentage of the unit B in thepolymer (a polyvinyl OH moiety or PVOH), and the acetate or estercontent is based on the weight percentage of unit C in the polymer.

Notably, for a given type of plasticizer, the compatibility of theplasticizer in the polymer is largely determined by the hydroxyl contentof the polymer. Polymers with greater residual hydroxyl content aretypically correlated with reduced plasticizer compatibility or capacity,typically due to the hydrophobicity of the plasticizer being morecompatible with fewer hydrophilic groups present on the polymer chain.Conversely, polymers with a lower residual hydroxyl content typicallywill result in increased plasticizer compatibility or capacity.Generally, this correlation between the residual hydroxyl content of apolymer and plasticizer compatibility/capacity can be manipulated andexploited to allow for addition of the proper amount of plasticizer tothe polymer resin and to stably maintain differences in plasticizercontent between multiple interlayers.

The hydroxyl group content of the poly(vinyl acetal) resin used to makethe composition is not particularly limited, but suitable amounts arefrom at least about 6, or at least about 8, or at least about 10, or atleast about 11, or at least about 12, or at least about 13, or at leastabout 14, or at least about 15, or at least about 16, or at least about17, and in each case up to about 35 wt. % PVOH. For example, suitableweight percent (wt. %) hydroxyl groups ranges calculated as PVOH includeabout 6 to 35, or 6 to 30, or 6 to 25, or 6 to 23, or 6 to 20, or 6 to18, or 6 to 17, or 6 to 16, or 6 to 15, or 7 to 35, or 7 to 30, or 7 to25, or 7 to 23, or 7 to 20, or 7 to 18, or 7 to 17, or 7 to 16, or 7 to15, or 8 to 35, or 8 to 30, or 8 to 25, or 8 to 23, or 8 to 20, or8to18, or8to 17, or8to 16, or8to 15, or 9 to 35, or 9 to 30, or 9 to 25, or9 to 23, or 9 to 20, or 9 to 18, or 9 to 17, or 9 to 16, or 9 to 15, or10 to 35, or 10 to 30, or 10 to 25, or 10 to 23, or 10 to 20, or 10 to18, or 10 to 17, or 10 to 16, or 10 to 15, or 11 to 35, or 11 to 30, or11 to 25, or 11 to 23, or 11 to 20, or 11 to 18, or 11 to 17, or 11 to16, or 11 to 15, or 12 to 35, or 12 to 30, or 12 to 25, or 12 to 23, or12 to 20, or 12 to 18, or 12 to 17, or 12 to 16, or 12 to 15, or 13 to35, or 13 to 30, or 13 to 25, or 13 to 23, or 13 to 20, or 13 to 18, or13 to 17, or 13 to 16, or 13 to 15, or 14 to 35, or 14 to 30, or 14 to25, or 14 to 23, or 14 to 20, or 14 to 18, or 14 to 17, or 14 to 16, or14 to 15, or 15 to 35, or 15 to 30, or 15 to 25, or 15 to 23, or 15 to20, or 15 to 18, or 15 to 17, or 15 to 16, or 16 to 35, or 16 to 30, or16 to 25, or 16 to 23, or 16 to 20, or 16 to 18, or 16 to 17, or 17 to35, or 17 to 30, or 17 to 25, or 17 to 23, or 17 to 20, or 17 to 18. Ifdesired, the hydroxyl number chosen can be on the lower end of theranges. In general, a poly(vinyl acetal) polymer having a lower hydroxylnumber has the capability of absorbing more plasticizer and absorbing itmore efficiently.

The poly(vinyl acetal) resin used to make the monolithic interlayercomposition or sheet can also comprise 20 wt. % or less, or 17 wt. % orless, or 15 wt. % or less of residual ester groups, including 13 wt. %or less, or 11 wt. % or less, or 9 wt. % or less, or 7 wt. % or less, or5 wt. % or less, or 4 wt. % or less residual ester groups calculated aspolyvinyl ester, e.g., acetate, with the balance being an acetal,preferably butyraldehyde acetal, but optionally including other acetalgroups in a minor amount, for example, a 2-ethyl hexanal group (see, forexample, U.S. Pat. No. 5,137,954, the entire disclosure of which isincorporated herein by reference). Suitable ranges of residual estergroups by wt. % include 0 to 20, or 0 to 17, or 0 to 15, or 0 to 13, or0 to 11, or 0 to 9, or 0 to 7, or 0 to 5, or 0 to 4, or 0 to 20, or 0 to17, or 0 to 15, or 0 to 13, or 0 to 11, or 0 to 9, or 0 to 7, or 0 to 5,or 0 to 4, or 1 to 20, or 1 to 17, or 1 to 15, or 1 to 13, or 1 to 11,or 1 to 9, or 1 to 7, or 1 to 5, or 1 to 4, or 1 to 20, or 1 to 17, or 1to 15, or 1 to 13, or 1 to 11, or 1 to 9, or 1 to 7, or 1 to 5, or 1 to4, or 2 to 20, or 2 to 17, or 2 to 15, or 2 to 13, or 2 to 11, or 2 to9, or 2 to 7, or 2 to 5, or 2 to 4, or 3 to 20, or3to 17, or3to 15,or3to 13, or 3 to 11, or 3 to 9, or 3 to 7, or 3 to 5, or 3 to 4, or 3to 20, or3to 17, or3to 15, or3to 13, or3to 11, or 3 to 9, or 3 to 7, or3 to 5, or 3 to 4, or 4 to 20, or 4 to 17, or 4 to 15, or 4 to 13, or 4to 11, or 4 to 9, or 4 to 7, or 4 to 5, or 6 to 20, or 6 to 17, or 6 to15, or 6 to 13, or 6 to 11, or 6 to 9. As with the residual hydroxylgroup measurement, the weight percent of residual ester groups (e.g.acetate) is based on the moiety in the polymer backbone onto which islinked the acetate group, including the pendant acetate group.

The poly(vinyl acetal) resin used in the invention can also have anacetal content of at least 50 wt. %, or at least 55 wt. %, or at least60 wt. %, or at least 65 wt. %, or at least 70 wt. %, or at least 75 wt.%, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, andin each case up to 94 wt. %. Suitable ranges include 50 to 94, or 50 to93, or 50 to 92, or 50 to 91, or 50 to 90, or 50 to 89, or 50 to 88, or50 to 86, or 50 to 85, or 55 to 94, or 55 to 93, or 55 to 92, or 55 to91, or 55 to 90, or 55 to 89, or 55 to 88, or 55 to 86, or 55 to 85, or60 to 94, or 60 to 93, or 60 to 92, or 60 to 91, or 60 to 90, or 60 to89, or 60 to 88, or 60 to 86, or 60 to 85, or 65 to 94, or 65 to 93, or65 to 92, or 65 to 91, or 65 to 90, or 65 to 89, or 65 to 88, or 65 to86, or 65 to 85, or 70 to 94, or 70 to 93, or 70 to 92, or 70 to 91, or70 to 90, or 70 to 89, or 70 to 88, or 70 to 86, or 70 to 85, or 75 to94, or 75 to 93, or 75 to 92, or 75 to 91, or 75 to 90, or 75 to 89, or75 to 88, or 75 to 86, or 75 to 85, 80 to 94, or 80 to 93, or 80 to 92,or 80 to 91, or 80 to 90, or 89 to 89, or 80 to 88, or 80 to 86, or 80to 85, 85 to 94, or 85 to 93, or 85 to 92, or 85 to 91, or 85 to 90, or85 to 89, or 85 to 88, or 85 to 86, or 90 to 94, or 90 to 93, or 90 to92.

The combination of OH, ester, and acetal ranges is not particularlylimited. Some of the range combinations can be those corresponding tothe checked boxes in Table 1 below.

TABLE 1 OH Ester wt % wt. % 0-20 1-20 2-17 2-15 2-13 2-8 2-6 3-20 3-153-11 3-9 4-20 4-17 4-15  6-25 X X X X X X X X X X X X X  7-25 X X X X XX X X X  8-25 X X X X X X  9-25 X X X 10-25 X X X  6-23 X X X X X X X XX X X X X  8-23 X X x X X  9-23 X X  6-20 X X X X X X X X X X X X X 8-20 X X x X X  9-20 X X 10-20 X X  6-18 X X X X X X X X X X X X X 9-18 X X 10-18 X X  6-15 X X X X X X X X X X X X X  8-15 X X X X X10-15 X X Acetal 50- 65- 70- 70- 90- 70- 75- 65- 70- 75- 65- 75- 70- 75-Wt. % 94 89 92 88 92 91 91 91 91 91 89 89 88 88

The acetal groups can be vinyl propynal groups, vinyl butyral groups,and the like, and are desirably vinyl butyral groups.

Conventional poly(vinyl acetal) resin for the typical industrialpoly(vinyl acetal) monolithic interlayer generally has a molecularweight (M_(w)) of greater than about 180,000, preferably about 185,000to about 250,000 Daltons, as measured by size exclusion chromatographyusing low angle laser light scattering (SEC/LALLS) method of Cotts andOuano in tetra-hydrofuran. However, we have found it beneficial to usepoly(vinyl acetal) resins having an Mw of 160,000 or less, or 155,000 orless, or 150,000 or less, or 145,000 or less, or 140,000 or less, or135,000 or less, or 130,000 or less, or 125,000 or less, or 120,000 orless, or 115,000 or less, or 110,000 or less, or 105,000 or less, or100,000 or less, or 95,000 or less, or 90,000 or less, or 85,000 orless, or 80,000 or less, and in each case, at least 45,000, or at least50,000. The term “molecular weight” means the weight average molecularweight (M_(w)). The method for determining the molecular weight as setforth in this description includes using hexafluorisopropanol as themobile phase (0.8 mL/minute). Each sample is prepared by weighingapproximately 20 milligrams of resin into a 25 mL flask and adding 10 mLof the mobile phase. The flask is then placed in an automated shakingdevice until the polymer is fully dissolved. The analysis is performedusing a three-detector system that includes a Viscotek GPCmax (with anautosampler, pump, and degasser), a Viscotek triple detector TDA302(RALL/LALLS, Viscometer, and DRI combination) with a column oven(commercially available from Malvern Instruments, Malvern, UK). Theseparation is performed by three Viscotek mixed bed columns, including atype I-MB (one low and two high range molecular weight) maintained at45° C. The complete detector set up is calibrated using a narrowpoly(methyl methacrylate) standard (commercially available fromViscotek) with a reported molecular weight of 93.458, an intrinsicviscosity of 0.615, and a differential index of refraction (dn/dc) valueof 0.1875. The refractive index of the mobile phase is 1.2649 and ado/dc value of 0.189 is used for PVB. Viscotek Omnisec 4.7.0 software(commercially available from Malvern Instruments) is used for datacalculations.

The lower molecular weight poly(vinyl acetal) resins that can be used inthe invention allow one to decrease the amount of plasticizer (whichwill increase the Tg of the poly(vinyl acetal) resin) while maintainingequivalent or lower extrusion pressures. By lowering the amount ofplasticizer used, the E′(storage) modulus can also be increased. Merelylowering the amount of plasticizer to increase the Tg of a conventionalmolecular weight poly(vinyl acetal) resin renders the resin toodifficult to process. Even though we do not see a necessary correlationbetween the molecular weight and the Tg of the poly(vinyl acetal) resinat equivalent plasticizer loadings, we have found that lowering themolecular weight of the poly(vinyl acetal) resin and lowering the amountof plasticizer allows one to adequately process thermoplastic resins athigh Tg values while also providing for an increased E′ modulus. Thus,we have found that it is desirable to employ a lower molecular weightpoly(vinyl acetal) resin for high Tg applications.

Examples of suitable Mw ranges include 45,000 to160,000, or 45,000 to155,000, or 45,000 to 150,000, or 45,000 to 145,000, or 45,000 to140,000, or 45,000 to 135,000, or 45,000 to 130,000, or 45,000 to125,000, or 45,000 to 120,000, or 45,000 to 115,000, or 45,000 to110,000, or 45,000 to 105,000, or 45,000 to 100,000, or 45,000 to95,000, or 45,000 to 90,000, 50,000 to160,000, or 50,000 to 155,000, or50,000 to 150,000, or 50,000 to 145,000, or 50,000 to 140,000, or 50,000to 135,000, or 50,000 to 130,000, or 50,000 to 125,000, or 50,000 to120,000, or 50,000 to 115,000, or 50,000 to 110,000, or 50,000 to105,000, or 50,000 to 100,000, or 50,000 to 95,000, or 50,000 to 90,000,or 60,000 to160,000, or 60,000 to 155,000, or 60,000 to 150,000, or60,000 to 145,000, or 60,000 to 140,000, or 60,000 to 135,000, or 60,000to 130,000, or 60,000 to 125,000, or 60,000 to 120,000, or 60,000 to115,000, or 60,000 to 110,000, or 60,000 to 105,000, or 60,000 to100,000, or 60,000 to 95,000, or 60,000 to 90,000, 70,000 to160,000, or70,000 to 155,000, or 70,000 to 150,000, or 70,000 to 145,000, or 70,000to 140,000, or 70,000 to 135,000, or 70,000 to 130,000, or 70,000 to125,000, or 70,000 to 120,000, or 70,000 to 115,000, or 70,000 to110,000, or 70,000 to 105,000, or 70,000 to 100,000, or 70,000 to95,000, or 70,000 to 90,000, 80,000 to160,000, or 80,000 to 155,000, or80,000 to 150,000, or 80,000 to 145,000, or 80,000 to 140,000, or 80,000to 135,000, or 80,000 to 130,000, or 80,000 to 125,000, or 80,000 to120,000, or 80,000 to 115,000, or 80,000 to 110,000, or 80,000 to105,000, or 80,000 to 100,000, or 80,000 to 95,000, or 80,000 to 90,000,90,000 to160,000, or 90,000 to 155,000, or 90,000 to 150,000, or 90,000to 145,000, or 90,000 to 140,000, or 90,000 to 135,000, or 90,000 to130,000, or 90,000 to 125,000, or 90,000 to 120,000, or 90,000 to115,000, or 90,000 to 110,000, or 90,000 to 105,000, or 90,000 to100,000, or 100,000 to 160,000, or 100,000 to 155,000, or 100,000 to150,000, or 100,000 to 145,000, or 100,000 to 140,000, or 100,000 to135,000, or 105,000 to 160,000, or 105,000 to 155,000, or 105,000 to150,000, or 105,000 to 105,000, or 105,000 to 140,000, or 105,000 to135,000, or 105,000 to 130,000, 110,000 to160,000, or 110,000 to155,000, or 110,000 to 150,000, or 110,000 to 145,000, or 110,000 to140,000, or 110,000 to 135,000, or 110,000 to 130,000.

The compositions of the invention are predominately poly(vinyl acetal)types of composition. In this regard, the compositions of the inventioncontain poly(vinyl acetal) in an amount of at least 60 wt. %, or atleast 65 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least80 wt. %, or at least 85 wt. %, or at least 90 wt. % or at least 95 wt.%, and in each case up to 98 wt. %. In each case, the poly(vinyl acetal)resin is desirably a polyvinyl butyral resin.

The composition of the invention also contains at least one plasticizer.Plasticizers work by embedding themselves between chains of polymers,spacing them apart (increasing the “free volume”) and thus significantlylowering the glass transition temperature (T_(g)) of the polymer resin(typically by 0.5 to 4° C./phr), making the material softer and moreflowable. In this regard, the amount of plasticizer in the interlayercan be adjusted to affect the glass transition temperature (T_(g))values. The glass transition temperature (T_(g)) is the temperature thatmarks the transition from the glassy state of the interlayer to theelastic state. In general, higher amounts of plasticizer loading willresult in lower T_(g). Conventional, previously utilized monolithicinterlayers generally have a T_(g) in the range of about 0° C. foracoustic (noise reducing) interlayer up to 46° C. for hurricane,structural and aircraft interlayer applications, which at the upper endof the Tg range are difficult to process. An interlayer's glasstransition temperature is also correlated with the stiffness of theinterlayer: the higher the glass transition temperature, the stiffer theinterlayer. Generally, an interlayer with a glass transition temperatureof 30° C. or higher increases laminated glass strength and torsionalrigidity. A softer interlayer (generally characterized by an interlayerwith a glass transition temperature of lower than 30° C.), on the otherhand, contributes to the sound dampening effect (i.e., the acousticcharacteristics).

The Tg of the interlayers of the invention advantageously have a Tg ofat least 46° C., or at least 46.5° C., or at least 47° C., or at least50.0° C., or at least 51° C., or at least 52° C., or at least 53° C., orat least 54° C., or at least 55° C., or at least 56° C., or at least 57°C., or at least 58° C., or at least 59° C., or at least 60° C. The upperlimit is not particularly limited. It can be up to 80° C., or up to 75°C., or up to 70° C., or up to 65° C. Suitable ranges include 46° C.-80°C., or 46° C-78° C., or 46° C-75° C., or 46° C-73° C., or 46° C-70° C.,or 46° C.-68° C., or 46° C-65° C., or 46° C-63° C., or 46.5° C-80° C.,or 46.5° C-78° C., or 46.5° C-75° C., or 46.5° C-73° C., or 46.5° C-70°C., or 46.5° C-68° C., or 46.5° C.-65° C., or 46.5° C-63° C., or 47°C-80° C., or 47° C-78° C., or 47° C-75° C., or 47° C.-73° C., or 47°C-70° C., or 47° C-68° C., or 47° C-65° C., or 47° C-63° C., or 50°C.-80° C., or 50° C-78° C., or 50° C-75° C., or 50° C-73° C., or 50°C-70° C., or 50° C.-68° C., or 50° C-65° C., or 50° C-63° C., 51° C-80°C., or 51° C-78° C., or 51° C-75° C., or 51° C-73° C., or 51° C-70° C.,or 51° C-68° C., or 51° C-65° C., or 51° C-63° C., 53° C-80° C., or 53°C-78° C., or 53° C-75° C., or 53° C-73° C., or 53° C-70° C., or 53°C-68° C., or 53° C-65° C., or 53° C-63° C., 55° C-80° C., or 55° C-78°C., or 55° C.-75° C., or 55° C-73° C., or 55° C-70° C., or 55° C-68° C.,or 55° C-65° C., or 55° C.-63° C., 57° C-80° C., or 57° C-78° C., or 57°C-75° C., or 57° C-73° C., or 57° C-70° C., or 57° C-68° C., or 57°C-65° C., or 57° C-63° C.

The glass transition temperature (Tg) is determined by rheornetricdynamic analysis using the following procedure. The poly(vinyl acetal)sheet is molded into a sample disc of 25 millimeters (mm) in diameter.The poly(vinyl acetal) sample disc is placed between two 25 mm diameterparallel plate test fixtures of a Rheometrics Dynamic Spectrometer II.The poly(vinyl acetal) sample disc is tested in shear mode at anoscillation frequency of 1 Hertz as the temperature of the poly(vinylacetal) sample is increased from −20 to 70° C. at a rate of 2°C./minute. The position of the maximum value of tan delta (damping)plotted as dependent on temperature is used to determine Tg. Experienceindicates that the method is reproducible to within +/−1° C.

As used herein, the amount of plasticizer, or any other component in theinterlayer, can be measured as parts per hundred parts resin (phr), on aweight per weight basis. For example, if 30 grams of plasticizer isadded to 100 grams of polymer resin, then the plasticizer content of theresulting plasticized polymer would be 30 phr. As used herein, when theplasticizer content of the interlayer is given, the plasticizer contentis determined with reference to the phr of the plasticizer in the meltthat was used to produce the interlayer.

The interlayer comprises at least 5, or at least 8, or at least 10, orat least 13, or at least 15, or at least 17, or at least 20, and up to28, or up to 25, or up to 23, or up to 20, or up to 18, or up to 17, orup to 15, or up to 13, or up to 10, or up to 9, or up to 8, or up to 7parts plasticizer per hundred parts of poly(vinyl acetal) resin (“phr”).Suitable ranges of plasticizer in phr within a layer include 5 to 28, or5 to 25, or 5 to 23, or 5 to 20, or 5 to less than 20, or 5 to 19, or 5to 18, or 5 to 17, or 5 to 15, or 5 to 13, or 5 to 10, or 5 to 9, or 5to 8, or 5 to 7, 8 to 28, or 8 to 25, or 8 to 23, or 8 to 20, or 8 toless than 20, or 8 to 19, or 8 to 18, or 8 to 17, or 8 to 15, or 8 to13, or 8 to 10, or 10 to 28, or 10 to 25, or 10 to 23, or 10 to 20, or10 to less than 20, or 10 to 19, or 10 to 18, or 10 to 17, or10 to 15,or 10 to 13, or 13 to 28, or 13 to 25, or 13 to 23, or 13 to 20, or 13to less than 20, or 13 to 19, or 13 to 18, or 13 to 17, or 13 to 15, or15 to 28, or 15 to 25, or 15 to 23, or 15 to 20, or 15 to less than 20,or 15 to 19, or 15 to 18, or 15 to 17, or 17 to 28, or 17 to 25, or 17to 23, or 17 to 20, or 17 to less than 20, or 17 to 19, or 17 to 18, 20to 28, or 20 to 25, or 20 to 23, or 23 to 28, or 23 to 25.

Since a reduction in the amount of plasticizer present in thecomposition of the invention contributes toward an increase in Tg andstiffness, it is desirable to use 20 or less, or less than 20, or 19 orless, or 18 or less, and at least 5 or at least 8, in each case partsplasticizer per hundred parts of poly(vinyl acetal) resin. For example,the amount of plasticizer is desirably 5 to 20, or 5 to less than 20, or5 to 19, or 5 to 18, or 5 to 17, or 5 to 16, or 5 to 15, or 8 to 20, or8 to less than 20, or 8 to 19, or 8 to 18, or 8 to 17, or 8 to 16, or 8to 15, or 10 to 20, or 10 to less than 20, or 10 to 19, or 10 to 18, or10 to 17, or 10 to 16, or 10 to 15, in each case parts per hundred partsof poly(vinyl acetal) resin. Any ranges at an upper end of less than 20phr are particularly desirable as these amounts tend to enhance the Tgof the interlayer.

The adjustments in the amount of plasticizer are made possible by theuse of polymers having a lower molecular weight, and the reduced amountof plasticizer allows one to make a higher Tg interlayer sheet, whilethe lower molecular weight poly(vinyl acetal) resin also allows one tomake the sheet at acceptable rates. The adjustment between the selectionof molecular weight and the amount of plasticizer allows one to takeadvantage of a variety of properties and opens up large processing andapplication windows. For example, if a particular application does notrequire a high end Tg, the invention allows one to increase the amountof plasticizer to further improve the flowability of the polymer andincrease the output (capacity) of the extruder while maintaining acompositional Tg of at least 46° C. Alternatively, with an increase inflowability, the capacity or output of the extruder can be maintainedconstant while decreasing the extrusion temperature, thereby saving onenergy costs. The extrusion temperature is the temperature of thepolymer at the entrance to the die head. If none of these objectives areparamount and maximizing the Tg of the interlayer is desired, as notedabove, the amount of plasticizer can be reduced to a lower end of therange, made possible with the use of lower molecular weight polymers,while maintaining reasonable polymer flowability at extrusiontemperatures not exceeding 240° C., or even not exceeding 235° C., oreven not exceeding 230° C. By maintaining extrusion temperatures notexceeding 240° C., the formation of undesirable degradation by-productsis minimized.

The type of plasticizer used is not particularly limited. Theplasticizer can be a compound having a hydrocarbon segment of 30 orless, or 25 or less, or 20 or less, or 15 or less, or 12 or less, or 10or less carbon atoms, and in each case at least 6 carbon atoms. Suitableconventional plasticizers for use in these interlayers include esters ofa polybasic acid or a polyhydric alcohol, among others. Suitableplasticizers include, for example, triethylene glycoldi-(2-ethylhexanoate) (“3GEH”), triethylene glycol di-(2-ethylbutyrate),triethylene glycol diheptanoate, tetraethylene glycol diheptanoate,dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate, diisononyladipate, heptylnonyl adipate, dibutyl sebacate, butyl ricinoleate,castor oil, dibutoxy ethyl phthalate, diethyl phthalate, dibutylphthalate, trioctyl phosphate, triethyl glycol ester of coconut oilfatty acids, phenyl ethers of polyethylene oxide rosin derivatives, oilmodified sebacic alkyd resins, tricresyl phosphate, and mixturesthereof. A desirable plasticizer is 3GEH.

High refractive index plasticizers may be used in the composition of theinvention, either alone or in combination with another plasticizer.Examples of the high refractive index plasticizers include, but are notlimited to, esters of a polybasic acid or a polyhydric alcohol,polyadipates, epoxides, phthalates, terephthalates, benzoates, toluates,mellitates and other specialty plasticizers, among others. Examples ofhigh refractive index plasticizers include, but are not limited to,dipropylene glycol dibenzoate, tripropylene glycol dibenzoate,polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexylbenzoate, diethylene glycol benzoate, propylene glycol dibenzoate,2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), ethoxylated nonylphenol, and mixtures thereof.Examples of more preferred high refractive index plasticizers aredipropylene glycol dibenzoates and tripropylene glycol dibenzoates.

In addition to the use of a plasticizer, various adhesion control agents(“ACAs”) can be used with the poly(vinyl acetal) resins and in thesheets of the invention. ACAs in the monolithic interlayer formulationcontrol adhesion of the sheet to glass to provide energy absorption onimpact of the glass laminate. In various embodiments of interlayers ofthe present disclosure, the interlayer can comprise about 0.003 to about0.15 parts ACAs per 100 parts resin; about 0.01 to about 0.10 parts ACAsper 100 parts resin; and about 0.01 to about 0.04 parts ACAs per 100parts resin. Such ACAs, include, but are not limited to, the ACAsdisclosed in U.S. Pat. No. 5,728,472 (the entire disclosure of which isincorporated herein by reference), residual sodium acetate, potassiumacetate, magnesium bis(2-ethyl butyrate), and/or magnesiumbis(2-ethylhexanoate).

Anti-blocking agents may also be added to the composition of the presentinvention to reduce the level of blocking of the interlayer.Anti-blocking agents are known in the art, and any anti-blocking agentthat does not adversely affect the properties of the interlayer may beused. A particularly preferred anti-blocking agent that can besuccessfully used as in the polymer sheet while not affecting opticalproperties of the sheet or the adhesive properties of the sheet to glassis a fatty add amide (see, for example, U.S. Pat. No.6,825,255, theentire disclosure of which is incorporated herein).

Other additives may be incorporated into the composition to enhance itsperformance in a final product and impart certain additional propertiesto the interlayer. Such additives include, but are not limited to, dyes,pigments, stabilizers (e.g., ultraviolet stabilizers), antioxidants,flame retardants, IR absorbers or blockers (e.g., indium tin oxide,antimony tin oxide, lanthanum hexaboride (LaB₆) and cesium tungstenoxide), processing aides, flow enhancing additives, lubricants, impactmodifiers, nucleating agents, thermal stabilizers, UV absorbers, UVstabilizers, dispersants, surfactants, chelating agents, couplingagents, adhesives, primers, reinforcement additives, and fillers, amongother additives known to those of ordinary skill in the art.

The monolithic interlayer composition has a melt flow index (“MFI”) ofat least 0.65 grams/10 minutes at 190° C. and under a load of 2.16kilograms. The molecular weight of the poly(vinyl acetal) resin and theamount of plasticizer can be adjusted to provide an MFI of at least0.65. At these MFI levels, the interlayer composition/moltenthermoplastic is reasonably flowable and within a commerciallyacceptable output during extrusion. The high MFI of the composition withlowered molecular weight resin provides a wider processing window whileproviding a sheet that has improved stiffness and Tg. The MFI is atleast 0.65, or can be at least 0.70, or at least 0.80, or at least 0.90,or at least 1, or at least 1.1, or at least 1.2, or at least 1.4, or atleast 1.5, or at least 1.8, or at least 2, or at least 3, or at least 5,or at least 7, or at least 10, each expressed as g/10 min. While thereis no particular upper limit, for practical considerations, such asretaining mechanical strength, the MFI should not exceed 40, or shouldnot exceed 30, or should not exceed 25, each expressed as g/10 min. Ifthe MFI is too low, processability becomes too difficult at commerciallyuseful rates. If the MFI is excessively high, the mechanical propertiesof the sheet can deteriorate to the extent that the monolithicinterlayer does not provide a commercially useful panel. Suitable rangesinclude 0.65-40, or 0.65-30, or 0.65-25, or 0.7-40, or 0.7-30, or0.7-25, or 0.8-40, or 0.8-30, or 0.8-25, or 0.9-40, or 0.9-30, or0.9-25, or 1-40, or 1-30, or 1-25, or 1.1-40, or 1.1-30, or 1.1-25, or1.2-40, or 1.2-30, or 1.2-25, or 1.4-40, or 1.4-30, or 1.4-25, or1.5-40, or 1.5-30, or 1.5-25, or 1.8-40, or 1.8-30, or 1.8-25, or 2-40,or 2-30, or 2-25, or 3-40, or 3-30, or 3-25, or 5-40, or 5-30, or 5-25,or 7-40, or 7-30, or 7-25, or 10-40, or 10-30, or 10-25. The MFI of thecomposition of the invention is determined according to ASTM D1238-13,Procedure A.

The monolithic interlayer composition can have a solution viscosity of120 cps or less. The molecular weight of the poly(vinyl acetal) resinand the amount of plasticizer can be adjusted to provide a solutionviscosity of the thermoplastic composition (that includes resin andplasticizer) of 125 cps or less. The solution viscosity as used hereinis determined by placing the sheet samples in a crucible overnight todry; determining the sheet sample weight by formula: Wt.sheet=3.195(100+phr)/100; placing the sheet in 4 oz. bottle with 39.57 gMethanol to dissolve; placing the bottle in a constant temperature waterbath at 20 +/−0.1 degree C. for 1 hour but not to exceed 1.5 hours,placing a viscometer (e.g. Cannon No. 400) in water bath for 5 min. toequilibrate, transferring 10 mls of solution to viscometer by pipette;and timing the solution flow between viscometer marks; then multiplyingthe time(sec.) with the Viscometer factor to determine viscosity in cps(1.038 for the Cannon No. 400). Suitable solution viscosities of theinterlayer composition and thermoplastic composition include, incentipoise, 125 or less, 120 or less, or 110 or less, or 100 or less, or90 or less, or 85 or less, or 80 or less, or 70 or less, or 65 or less,or 60 or less, or 55 or less, or 50 or less, or 45 or less, or 40 orless, or 35 or less, or 30 or less. Additionally or in the alternative,the solution viscosity is at least 5 cps, or at least 10 cps. Suitableranges of solution viscosity include, in cps, 5-125, or 10-125, or5-120, or 10-120, or 5-110, or 10-110, or 5-100, or 10-10, or 5-95, or10-95, or 5-90, or 10-90, or 5-85, or 10-85, or 5-80, or 10-80, or 5-70,or 10-70, or 5-65, or 10-65, or 5-60, or 10-60, or 5-55, or 10-55, or5-50, or 10-50, or 5-45, or 10-45, or 5-40, or 10-40, or 5-35, or 10-35,or 5-30, or 10-30.

Co-additives such as anti-blocking agents, colorants and UV inhibitors(in liquid, powder, or pellet form) are often used and can be mixed intothe thermoplastic resin or plasticizer prior to arriving in the extruderdevice or combined with the thermoplastic resin inside the extruderdevice. These additives are incorporated into the thermoplasticcomposition, and by extension the resultant monolithic interlayer sheet,to enhance certain properties of the interlayer sheet and itsperformance in a multiple layer glass panel product (or photovoltaicmodule).

Any of the compositions of the invention described above can comprise amonolithic interlayer sheet.

The monolithic interlayer sheet can be made by any suitable processknown to one of ordinary skill in the art of producing interlayersheets. For example, it is contemplated that the monolithic interlayersheets may be formed through dipcoating, solution casting, compressionmolding, injection molding, melt extrusion, melt blowing or any otherprocedures for the production and manufacturing of an interlayer sheetknown to those of ordinary skill in the art.

In one method, the monolithic interlayer sheets can be made by anyconventional sheet extrusion device. The extruder can be a single ortwin screw extruder. There is now also provided a process in which amonolithic poly(vinyl acetal) sheet can be made by:

-   -   (i) providing an extrusion system comprising die and an extruder        having a barrel;    -   (ii) feeding a poly(vinyl acetal) resin and a plasticizer into        the barrel and passing a molten thermoplastic composition        comprising said poly(vinyl acetal) resin and plasticizer through        the extruder and the die to produce an extruded sheet, wherein        the melt flow index of said molten thermoplastic resin is at        least 0.65 g/10min when measured at 190° C. at a loading of 2.16        kilograms, and    -   (iii) cooling said sheet to produce a monolithic interlayer        sheet having a Tg of at least 46.0° C.

Reference to FIG. 2 is made to further illustrate the process of theinvention along with additional features.

As illustrated, there is provided an extrusion system made up of anextruder 1, a filter 2, a die 4, and a melt pump 3 disposed between thefilter 2 and the die 4.

In the extruder device 1, the particles of the thermoplastic composition10 comprising poly(vinyl acetal) resin and plasticizers, and otheradditives described above, are fed through a feed system 11 (e.g.hopper) into the barrel 12 of the extruder 1 and heated by heatingelements 13 to form a molten thermoplastic composition in the barrel 12that is generally uniform in temperature and composition. Generally, inthe extrusion process, thermoplastic resin and plasticizers, includingany of those resins and plasticizers described above, are pre-mixed andfed into an extruder device. For example, the process of the inventioncan include feeding a pre-mix into an extruder 1, wherein the pre-mix isobtained by combining a thermoplastic poly(vinyl acetal) resin and aplasticizer, and optionally other additives first to make a pre-mix, andfeeding the pre-mix to the barrel 12. This method is particularly usefulwhen using a single screw extruder. Alternatively, there can be providedat least two streams fed to the barrel 12 of an extruder (not shown),one stream comprising a poly(vinyl acetal) thermoplastic resin and asecond stream comprising a plasticizer, combining the two streams insidethe barrel of an extruder. This technique is particularly useful whenusing a twin-screw extruder. The at least two streams can be combinedinside the extruder by melting the poly(vinyl acetal) resin inside theextruder in the presence of the plasticizer.

The thermoplastic particles are propelled down the barrel 12 through theaction of the rotating screw 14 powered by a motor 15, and with acombination of shear forces and heat, melts the thermoplastic solidswithin the barrel 12 into a molten thermoplastic composition that ispropelled through a filter 2 to filter out particles. Passage through afilter 2 is a cause for pressure drop, and to compensate, a melt pump 3,such as a gear pump, can be located between the filter 2 and die 4. Theextruder die 4 is the component of the thermoplastic extrusion processwhich gives the final monolithic interlayer sheet product its profile. Aplurality of shapes can be imparted to the end monolithic interlayersheet by the die so long as a continuous profile is present.

The thermoplastic composition of the invention is desirably brought to atemperature of 240° C. or less within the barrel 12. When thecomposition experiences temperatures higher than 240° C., there isgenerally a risk of significant build-up of yellow color becausepoly(vinyl acetal) resins tend to form decomposition by-products athigher temperatures. The molten thermoplastic polymer composition isdesirably brought to a temperature within the barrel 12 of 240° C. orless, or 238° C. or less, or 235° C. or less, or 233° C. or less, or232° C. or less, or 230° C. or less, or 228° C. or less, or 226° C. orless, or 225° C. or less, or 220° C. or less, and in each case at atemperature of at least 150° C.

The molten thermoplastic composition is fed from the outlet 16 of themelt pump 3 and fed through a line 17 to a die 4. In this illustration,the thermoplastic composition experiences a pressure drop between theoutlet 16 of the melt pump and the exit to the die 4, and the magnitudeof the pressure drop affects the throughput and capacity of theextrusion process. As the flowability of the thermoplastic compositionincreases so does the throughput of the extrusion device. Theflowability of the thermoplastic composition will manifest itself by thepressure drop between the melt pump and the exit of the die. Since thethermoplastic compositions of the invention are flowable even with lowamounts of plasticizer made possible by the use of low Mw poly(vinylacetal) resins, it is now possible to process the thermoplastic resin ina commercially acceptable manner while obtaining an interlayer sheethaving high Tg. In the process of the invention, a reasonable pressuredrop across the melt pump outlet and the die exit is obtainable whilesimultaneously obtaining an interlayer sheet having a Tg of 46 or moreor 50.0° C. or more made at acceptable extrusion rates.

The flowability of the thermoplastic composition in the extruder can beexpressed as a composition having a high MFI at the conditions in theextruder. The MFI of the thermoplastic composition in the process of theinvention can be at least 0.65 grams/10min when measured at 190° C. at aloading of 2.16 kilograms.

The monolithic interlayer at the state after the extrusion die forms themelt into a continuous profile will be referred to as an “extrudedsheet.” At this stage in the process, the extrusion die has imparted aparticular profile shape to the thermoplastic composition, thus creatingthe extruded sheet. The extruded sheet is highly viscous throughout. Atleast a portion or the whole of the extruded sheet as it exits the dieis molten. In the extruded sheet, the thermoplastic composition as itexits the die has not yet been cooled to a temperature at which thesheet generally completely “sets.” Thus, after the extruded sheet leavesthe extrusion die, generally the next step is to cool the polymer meltsheet with a cooling device 5 to make a monolithic interlayer sheethaving a Tg of at least 46.0° C. Cooling devices include, but are notlimited to, spray jets, fans, cooling baths, and cooling rollers. Thecooling step functions to set the extruded sheet into a monolithicinterlayer sheet of a generally uniform non-molten cooled temperature.In contrast to the extruded sheet, this monolithic interlayer sheet isnot in a molten state. Rather, it is the set final form cooledmonolithic interlayer sheet product. Once the interlayer sheet has beencooled and set, it is cut with knives 6 and pulled through with aroller/winding system 7.

The thickness, or gauge, of the monolithic interlayer sheet is notparticularly limited and will depend upon the desired application.Examples of suitable thicknesses where the application will only utilizea monolithic interlayer sheet in a glass panel are at least 5 mils, orat least 10 mils, or at least 15 mils, and can be as thick as desired.The sheet can be as thick as 90 mils, or 120 mils, or more depending onthe desired application. Examples of ranges include from about 5 mils to120 mils (0.12 mm to 3.03 mm), or 15 mils to 90 mils (about 0.38 mm toabout 2.286 mm), or about 30 mils to about 60 mils (about 0.762 to 1.52mm), or about 15 mils to about 35 mils (about 0.375 to about 0.89 mm).In other applications, the thickness, or gauge, of the monolithicinterlayer sheet can be greater than 60 mils (1.52 mm) as desired forthe particular application.

As used herein, a multiple layer panel can comprise a single substrate,such as glass, acrylic, or polycarbonate with a monolithic interlayersheet disposed thereon, and most commonly, with a thin polymer filmfurther disposed over the monolithic interlayer. The combination ofmonolithic interlayer sheet and polymer film is commonly referred to inthe art as a bilayer. A typical multiple layer panel with a bilayerconstruct is: (glass)//(monolithic interlayer sheet)//(polymer film).The polymer film supplies a smooth, thin, rigid substrate that affordsbetter optical character than that usually obtained with a monolithicinterlayer sheet alone and functions as a performance enhancing layer.Polymer films differ from monolithic interlayer sheets, as used herein,in that polymer films are not poly(vinyl acetal) films and do notthemselves provide the necessary penetration resistance and glassretention properties, but rather provide performance improvements, suchas infrared absorption characteristics. Poly(ethylene terephthalate)(“PET”) is the most commonly used polymer film. Generally, a polymerfilm is thinner than a polymer sheet. The polymer film typically has athickness from about 0.001 to 0.2 mm thick.

Further, the multiple layer panel can be double paned with a constructsuch as: (glass)//(monolithic interlayer)//(glass); or(glass)//(monolithic interlayer)//polymer film//(monolithicinterlayer)//(glass).

The interlayers of the present disclosure will most commonly be utilizedin multiple layer panels comprising two substrates, preferably a pair ofglass sheets, with the interlayers disposed between the two substrates.An example of such a construct would be: (glass)//(monolithic interlayersheet)//(glass), where the monolithic interlayer sheet can comprisemultilayered interlayers, as noted above, and wherein at least one ofthe interlayers comprises a poly(vinyl acetal) sheet made by the methodof the invention.

The typical glass lamination process comprises the following steps: (1)assembly of the two substrates (e.g., glass) and interlayer; (2) heatingthe assembly via an IR radiant or convective means for a short period;(3) passing the assembly into a pressure nip roll for the firstdeairing; (4) heating the assembly a second time to about 50° C. toabout 120° C. to give the assembly enough temporary adhesion to seal theedge of the interlayer; (5) passing the assembly into a second pressurenip roll to further seal the edge of the interlayer and allow furtherhandling; and (6) autoclaving the assembly at temperatures between 135°C. and 150° C. and pressures between 150 psig and 200 psig for about 30to 90 minutes.

Other means for use in de-airing of the interlayer-glass interfaces(steps 2 to 5) known in the art and that are commercially practicedinclude vacuum bag and vacuum ring processes in which a vacuum isutilized to remove the air.

An alternate lamination process involves the use of a vacuum laminatorthat first de-airs the assembly and subsequently finishes the laminateat a sufficiently high temperature and vacuum.

Since the monolithic interlayer sheets have such a high Tg, theapplication windows open up to allow for their use in a wider variety ofapplications. For example, the monolithic interlayer can be used indemanding structural applications, especially where the temperatures mayexceed room temperature (25-30° C.). Examples include ballustrades,curtain walls, flooring, and the like

The monolithic interlayer of the invention also can now be used inapplications which require maintaining good modulus at highertemperatures, such as outdoor applications that undergo regularintermittent stresses, caused by such factors as walking or running, orthat are load bearing under temperature conditions that may exceed 35°C. Examples of applications in which the monolithic interlayer of theinvention is suited include outdoor stairs, outdoor platforms, pavementor sidewalk skylights, and the like.

The monolithic interlayer of the invention desirably has a storagemodulus E′ at 40° C. of at least 300,000,000 pascals, or at least400,000,000 pascals, or at least 500,000,000 pascals, or at least600,000,000 pascals, or at least 700,000,000 pascals, or at least800,000,000 pascals. There is no particular upper limit, althoughpractically the monolithic interlayer can obtain an E′ modulus as highas 3,000,000,000 pascals, or as high as 2,000,000,000 pascals, or ashigh as 1,500,000,000 pascals at 40° C.

The monolithic interlayer of the invention desirably also, or in thealternative, has a storage modulus E′' at 50° C. of at least 6,000,000pascals, or at least 7,000,000 pascals, or at least 8,000,000 pascals,or at least 9,000,000 pascals, or at least 10,000,000 pascals, or atleast 20,000,000 pascals, or at least 30,000,000 pascals, or at least40,000,000 pascals, or at least 50,000,000 pascals, or at least60,000,000 pascals, or at least 70,000,000 pascals, or at least80,000,000 pascals, or at least 90,000,000 pascals, or at least100,000,000 pascals. There is no particular upper limit, althoughpractically the monolithic interlayer can obtain an E′ modulus as highas 1,000,000,000 pascals, or as high as 900,000,000 pascals, or as highas 800,000,000 pascals at 50° C.

The storage E′ modulus of the monolithic interlayer is measuredaccording to ASTM D5026-06 (Reapproved 2014). The E′ modulus is obtainedby the Dynamic Mechanical Analysis using the RSA-II instrument. A 9 mmwide and 0.765 mm thick sample is clamped at the top and bottom andplaced in tension. The length of the sample between the clamps is 22 mm.A sinusoidal tensile strain of magnitude 0.01% is applied at a frequencyof 1 Hz to the specimen over a range of temperatures and the resultingstress response is measured. Modulus which is a measure of resistance ofthe material to deformation is obtained from the ratio of stress tostrain. For an oscillatory tensile deformation, E′ is the real part ofthe complex modulus and is referred to as the storage modulus.Temperature control is provided by an oven chamber and the heating rateis 3C./minute.

Glass panels made with the monolithic interlayers of the invention havethe capability of maintaining acceptable levels of creep resistance,which is 1 mm or less, even at the low poly(vinyl acetal) resinsmolecular weights. Glass panels containing the monolithic interlayers ofthe invention can exhibit a creep of not more than 1 mm at 100° C. andat 1000 hours, or nor more than 0.9 mm, or not more than 0.8 mm, or notmore than 0.7 mm, or not more than 0.6 mm, or not more than 0.5 mm, ornot more than 0.4 mm.

The method for determining creep resistance is to laminate themonolithic interlayer between two sheet of glass, one sheet measuring6″×6″ and the other 6″×7″. The glass panel test specimen is hung by theexposed 1″ section of glass in an oven set at 100° C. The test specimenis then removed at the predetermined intervals and measured to determinehow much of the 6″×6″ piece of glass has slipped down from its originalposition relative to the 6″×7″ glass. The predetermined intervals are at100, 250, 500, and 1000 hours.

EXAMPLES

A laboratory extrusion trial was conducted using a 1.25″ extruderoutfitted with an extrusion die. The extrusion system is outfitted witha filter at the head of the extruder, followed by a gear pump, followedby the die, and the speed of the gear pump was held constant at 44 rpmfor all examples. The extrusion rate was measured over the course of thetest and was approximately 47-48 g/min for all examples.

S-2075 plasticizer (3GEH) was used in all cases, at varying levels asdescribed in the table below. The same amount of adhesion control agentswas added in all cases in the premix.

Pressure transducers were mounted at the outlet of the gear pump. Thepressure at the gear pump relative to the control illustrates the effectof lowering the molecular weight of the PVB resin.

A control Saflex™ DG41 sheet was used to measure Tg and compare with theexperimental cases. Saflex™ DG41 is a commercial product for structuralapplications, and was used because it is available in the marketplace.

Table 2 below lists the effect of resin type and plasticizer loading onthe pressure at the outlet of the gear pump, as well as the Tg of theinterlayer for each case. The gear pump pressure is an indicator of animprovement in flowability of the thermoplastic resin in an extrusionenvironment.

TABLE 2 PVB Gear Glass Resin Pump Transition Weight Plasti- OutletTemper- MFI Average cizer Pressure ature (190/ Solution Example MW (phr)(psi) Tg (° C.) 2.16) Viscosity 1 (control) 170 20 4466 46.1 0.57 155Saflex ™ DG41 2 (control) 170 20 4240 46.2 Not Not analyzed analyzed 3130 20 3000 45.8 1.40 84.3 4 130 15 3700 51.5 1.03 97.6 5 130 10 439058.8 0.70 82.4 6 50 10 920 60.1 20 14.9

It can be seen that Example 2 demonstrates essentially the same glasstransition temperature as the control sheet of Example 1 (46.2° C. v.46.1° C.). Example 3 demonstrates almost the same glass transitiontemperature (45.8° C.) as Examples 1 and 2, showing that Tg is not afunction of the molecular weight of the poly(vinyl acetal) resin.Similarly, a comparison of Example 5 and Example 6 also demonstratesthat the Tg is not a function of the resin molecular weight since bothare plasticized at the same level (10 phr) and have similar Tg (58.8° C.v. 60.1° C.).

However, the examples do demonstrate that with a lower molecular weightresin, the amount of plasticizer can be reduced, which in turn elevatesthe Tg of the composition, and that this can be achieved at acceptablerates (as indicated by the lower pressure drop). Examples 4, 5 and 6,which employ a lower MW resin and lower amounts of plasticizer, producea sheet having a high Tg exceeding 50° C. In addition, the increase inTg is not at the expense of acceptable rates as indicated by pressuredrops at about the same amount as the control or lower.

Example 3, with a lower MW resin and equivalent plasticizer as Examples1 and 2, demonstrates that the molecular weight of the resin allows fora lower pressure at the gear pump due to improved flowability asindicated by its higher MFI value of 1.4 (compared to Example 1 at0.57). Example 6 also demonstrates the same point where the pressurereduction at the gear pump is about 79% relative to Example 1 due to itsdramatically higher MFI at 20 and about 78% relative to Example 2.

Examples 4, 5 and 6 demonstrate that higher Tg monolithic poly(vinylacetal) interlayers can be extruded at lower or almost equivalentpressure drop as Example 2. As the pressure at the gear pump starts toincrease due to further drops in the plasticizer level as can be seen inExample 5, the flowability of the thermoplastic resin can be improved bycontinuing to lower the molecular weight of the resin to compensate forthe low plasticizer levels as seen in Example 6. This effect can be seenin Example 6 that has the same low plasticizer level as Example 5, yethas a significantly improved flowability as indicated by its lowpressure requirement and higher MFI, compared to all other examples, atthe gear pump due to the reduction in molecular weight.

The examples 3-6 indicate the effect of improved flowability by higherMFI values compared to the control Examples 1 employing a resin ofhigher Mw. While the MFI starts to decrease as the amount of plasticizeris lowered (examples 3-5), the MFI remains higher than the control andcan be dropped further by employing a resin of lower Mw at the lowplasticizer levels.

Finally, the very low pressure of Example 6 suggests that the resin ofExample 6 can be used in blends with higher molecular weight resins tocontrol process conditions while achieving a higher Tg product.

The rheological properties of the interlayer sheets made in Examples 1-6were also studied. FIG. 1 shows that the sheets of Examples 3, 4, 5 and6 possess significantly higher storage modulus E′ at all temperatures of30° C. or more, such as at 40° C. and 50° C. and within the range of30-65° C., or 30-60° C., or 30-55° C., and the differences were quitelarge at 40-55° C., or 40-50° C. The modulus is also higher attemperatures of 50-55° C., suggesting that these formulations performbetter than control Examples 1 and 2 in structural applications that maybe exposed to higher than room temperature conditions.

Each of the examples 1-6 were subjected to the creep resistance testdescribed above. The results are set forth as illustrated graphically inFIG. 3. As can be seen from FIG. 3, all test specimens made from theinterlayers of the invention (3-6) maintained a creep resistance ofunder 1 mm in spite of using lower Mw poly(vinyl butyral) resins.

It is intended that the invention not be limited to the particularembodiments disclosed as the best mode contemplated for carrying outthis invention, and that the invention will include all embodimentsfalling within the scope of the appended claims.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present inventioncan be used interchangeably with any ranges, values, or characteristicsgiven for any of the other components of the invention, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout.

What we claim is:
 1. A monolithic interlayer sheet formed from acomposition comprising: (A) poly(vinyl acetal) resin in an amount of atleast 60 wt. % based on the weight of the composition, wherein the Mw ofthe poly(vinyl acetal) resin does not exceed 150,000; and (B) aplasticizer in an amount of from 5 to 20 parts per one hundred parts ofsaid poly(vinyl acetal) resin; wherein said interlayer sheet has a Tg ofat least 46° C. and a melt flow index (“MFI”) of at least 0.65 grams/10minutes when measured at 190° C. at a load of 2.16 kilograms, andwherein the interlayer sheet has a modulus E′ at 40° C. of at least400,000,000 pascals and has a thickness of at least 5 mils.
 2. Theinterlayer sheet of claim 1, wherein said composition has a Tg of atleast 50° C.
 3. The interlayer sheet of claim 1, wherein saidcomposition has a Tg of at least 55° C.
 4. The interlayer sheet of claim1, wherein said composition has an MFI of at least 0.9.
 5. Theinterlayer sheet of claim 1, wherein said composition has an MFI of atleast 1.2.
 6. The interlayer sheet of claim 1, wherein said compositioncontains at least 80 wt. % poly(vinyl acetal) resin.
 7. The interlayersheet of claim 1, wherein the Mw of the poly(vinyl acetal) resin doesnot exceed 140,000.
 8. The interlayer sheet of claim 1, wherein the Mwof the poly(vinyl acetal) resin does not exceed 130,000.
 9. Theinterlayer sheet of claim 1, wherein the Mw of the poly(vinyl acetal)resin does not exceed 110,000.
 10. The interlayer sheet of claim 1,wherein the poly(vinyl acetal) resin has a solution viscosity of no morethan 120 cps.
 11. The interlayer sheet of claim 1, wherein the sheet hasa modulus E′ at 50° C. of at least 10,000,000 pascals.
 12. Theinterlayer sheet of claim 1, wherein the sheet has a thickness of atleast 30 mils.
 13. The interlayer sheet of claim 1, wherein thecomposition has a solution viscosity of not greater than 100 cps. 14.The interlayer sheet of claim 1, wherein the sheet is laminated between:(A) a layer of glass and a polymer film, and wherein said polymer filmis not a poly(vinyl acetal) resin; or (B) two layers of glass.
 15. Aglass panel comprising: (A) a first glass layer; (B) the monolithicinterlayer sheet of claim 1; and (C) second glass layer.
 16. The glasspanel of claim 15, wherein the glass panel exhibits a creep resistanceof not more than 1 mm when measured at 100° C. after 1000 hours.
 17. Amonolithic interlayer sheet formed from a composition comprising: (A)poly(vinyl butyral) resin in an amount of at least 60 wt. % based on theweight of the composition, wherein the Mw of the poly(vinyl butyral)resin does not exceed 130,000; and (B) a plasticizer in an amount offrom 10 to 20 parts per one hundred parts of said poly(vinyl butyral)resin; wherein said interlayer sheet has a Tg of at least 46° C. and amelt flow index (“MFI”) of at least 0.65 grams/10 minutes when measuredat 190° C. at a load of 2.16 kilograms, and wherein said interlayersheet has a modulus E′ at 40° C. of at least 400,000,000 pascals and hasa thickness of at least 5 mils.
 18. The interlayer sheet of claim 17,wherein the Mw of the poly(vinyl acetal) resin does not exceed 110,000.19. A glass panel comprising: (A) a first glass layer; (B) themonolithic interlayer sheet of claim 17; and (C) second glass layer. 20.The glass panel of claim 19, wherein the glass panel exhibits a creepresistance of not more than 1 mm when measured at 100° C. after 1000hours.